Conventionally, there is known a device described in the Japanese Patent Laid Open Gazette 2001-221627 as a device measuring a tilt angle of a measuring object. With regard to the device described in the Japanese Patent Laid Open Gazette 2001-221627, an angle gauge head is pivotally supported rotatably and the rotation angle of the angle gauge head is detected by a sensor. The shape of the angle gauge head is like a circle cut off a part thereof so as to have a major arc, and the angle gauge head touches the measuring object at its chord.
As a device measuring an attachment angle between an axle carrier and an absorber (for example, a camber angle), there is known an attachment angle measuring device 500 shown in FIG. 5.
The attachment angle measuring device 500 measures an attachment angle between an axle carrier 10 and an absorber 20, and comprises a carrier clamp 510 and a magnet scale 520.
The axle carrier 10 comprises an axle hub 11 and an axle housing 12, and supports a wheel (not shown) rotatably.
The axle hub 11 is fixed to the wheel. The axle housing 12 pivotally supports the axle hub 11 rotatably. An attachment bracket 12a is formed in the axle housing 12, and two holes respectively penetrated by bolts 31 and 32 are formed in the attachment bracket 12a. 
The absorber 20 comprises an absorber main body 21 and an absorber rod 22, and absorbs shock transmitted from the wheel to a main body of a vehicle.
The absorber main body 21 is cylindrical and one of ends (lower end) thereof is closed. An attachment bracket 21a is formed at the end (lower end) of the absorber main body 21. Two holes into which the bolts 31 and 32 are respectively inserted are formed in the attachment bracket 21a. 
The attachment bracket 21a of the absorber main body 21 and the attachment bracket 12a of the axle housing 12 are superimposed on each other so that the two holes formed in the attachment bracket 21a are respectively in agreement with the two holes formed in the attachment bracket 12a. The bolts 31 and 32 are respectively inserted into the holes and nuts (not shown) are screwed onto the bolts 31 and 32 so as to attach the absorber 20 to the axle carrier 10.
The absorber rod 22 is round bar-like shaped and slidably inserted into the absorber main body 21. A piston (not shown) is provided at one of ends (lower end) of the absorber rod 22 and is slid while touching an inner peripheral surface of the absorber main body 21. The other end (upper end) of the absorber rod 22 is projected upward from the absorber main body 21. The middle portion of the absorber rod 22 is sealingly and slidably supported by a through-hole formed in a lid 21b screwed onto the other end (upper end) of the absorber main body 21.
The inner space of the absorber main body 21 is filled with pressure oil. When the absorber rod 22 is slid about the absorber main body 21, pressure oil is moved between the portion of the inner space of the absorber main body 21 upper than the piston and the portion thereof lower than the piston through a hole formed in one of ends (lower end) of the absorber rod 22. By viscosity resistance of pressure oil at the time of passing through the hole formed in the piston, the absorber 20 absorbs shock transmitted from the wheel to the main body of the vehicle.
The carrier clamp 510 fixes the axle carrier 10 at the posture at which an axis 1 of the axle carrier 10 is in parallel to a horizontal plane (the posture similar to the final state of attached to the main body of the vehicle.
The carrier clamp 510 comprises a claw 511 and a claw 512. The distance (interval) between the claw 511 and the claw 512 is varied by operation of a hydraulic actuator.
When the axle carrier 10 is arranged between the claw 511 and the claw 512 and the distance between the claw 511 and the claw 512 is reduced, the axle carrier 10 is pinched by the claws 511 and 512.
The magnet scale 520 comprises a frame 521, a slide rod 522, a spring 523, a magnetic tape 524 and a magnetic flux response detecting head 525.
The frame 521 is a main structure of the magnet scale 520 and is fixed to another structure (not shown).
The slide rod 522 is bar-like shaped and slidably supported by the frame 521. A touching head 522a is provided at one of ends of the slide rod 522. The touching head 522a is substantially conical and a bottom surface of the touching head 522a is fixed to one of end surfaces of the slide rod 522. The diameter of the bottom surface of the touching head 522a is longer than that of the slide rod 522. A top of the touching head 522a touches an outer peripheral surface of the absorber main body 21.
The spring 523 is a helical spring engaged with the outside of the slide rod 522. One of ends of the spring 523 touches the bottom surface of the touching head 522a, and the other end of the spring 523 touches the frame 521. Therefore, the touching head 522a is biased toward the absorber main body 21 by the elastic force of the spring 523.
The magnetic tape 524 is a tape of a ferromagnetic substance stuck on an outer peripheral surface of the slide rod 522, and has memory so as to arrange magnetic signals (north poles and south poles) mutually at a fixed cycle in the slide direction (longer direction) of the slide rod 522.
The magnetic flux response detecting head 525 is disposed so as to face the magnetic tape 524 stuck on the outer peripheral surface of the slide rod 522. The magnetic flux response detecting head 525 comprises an exciting coil and a detecting coil. Alternating current flows in the exciting coil of the magnetic flux response detecting head 525 so as to excite the exciting coil.
When the touching head 522a touches the outer peripheral surface of the absorber main body 21 and the slide rod 522 is slid oppositely to the biasing force of the spring 523, the position of the magnetic tape 524 facing the magnetic flux response detecting head 525 is varied and the magnitude of the magnetic field around the exciting coil of the magnetic flux response detecting head 525 is varied. The detecting coil of the magnetic flux response detecting head 525 detects the variation of the magnitude of the magnetic field around the exciting coil as induced voltage so as to detect the amount of slide of the slide rod 522.
The attachment angle measuring device 500 calculates the attachment angle between the axle carrier 10 and the absorber 20 based on the amount of slide of the slide rod 522 detected by the magnet scale 520.
However, with regard to the attachment angle measuring device 500, it is difficult to measure the measurement of the attachment angle between the axle carrier 10 and the absorber 20 accurately. That is because following reason.
A piston provided at one of ends of the absorber rod 22 slidably touches the inner peripheral surface of the absorber main body 21. Therefore, the processing of the inner peripheral surface of the absorber main body 21 is accurate.
On the other hand, any member does not slidably touch the outer peripheral surface of the absorber main body 21. Therefore, the processing of the outer peripheral surface of the absorber main body 21 is not more accurate than that of the inner peripheral surface of the absorber main body 21, and dimensions of the processing of the outer peripheral surface of the absorber main body 21 are not uniform individually.
Accordingly, with regard to the attachment angle measuring device 500, the touching head 522a touches the outer peripheral surface of the absorber main body 21 whose processing is not accurate relatively, whereby it is difficult to measure the measurement of the attachment angle between the axle carrier 10 and the absorber 20 accurately.
A bracket or the like, which fixes piping (a flexible hose) supplying pressure oil so as to actuate a brake, is welded to the outer peripheral surface of the absorber main body 21. The attachment position of such a bracket is different for the type of the vehicle. Then, depending on the type of the vehicle, the bracket may interfere with the magnet scale 520. When weld spatter sticks on the outer peripheral surface of the absorber main body 21 at the time of welding the bracket, the weld spatter may touch the touching head 522a so as to reduce the accuracy of the measurement.
For solving the above problems, it is conceivable to make the touching head 522a touch an outer peripheral surface of the absorber rod 22 whose processing is accurate because the outer peripheral surface of the absorber rod 22 is slidably and liquid-sealingly supported by the through-hole formed in the lid 21b. 
The touching head 522a of the magnet scale 520 pushes the absorber rod 22 laterally with certain force. Then, especially in the case that the projection amount of the absorber rod 22 from the absorber main body 21 is large, the absorber rod 22 may be tilted against the absorber main body 21 about the point at which the absorber rod 22 touches the lid 21b. Accordingly, it is difficult to measure the measurement of the attachment angle between the axle carrier 10 and the absorber 20 accurately.
The sectional shape of the outer peripheral surface of the absorber rod 22 is a circle whose diameter is relatively small. Accordingly, it is difficult to make a peaked tip of the touching head 522a touch accurately a predetermined position on the outer peripheral surface of the absorber rod 22 (the position at which the axis of the slide rod 522 intersects the axis of the absorber rod 22), whereby works incidental to the fixation of the axle carrier 10 such as a positioning work are troublesome.
Therefore, at the process of attaching the absorber 20 to the axle carrier 10, it is difficult to adopt the attachment angle measuring device 500 to total inspection.
Furthermore, generally in the contact type measurement, increase of the number of measurement causes abrasion of the tip of the touching head 522a so as to reduce the accuracy of measurement.